Electric glass furnace structure

ABSTRACT

An electric glass furnace chamber having a bottom floor and side walls wherein the floor of the furnace is formed with a cruciform system of channels by means of which molten glass is withdrawn towards an outlet by opposing flow patterns in the channels thereby reducing flow patterns in the molten glass above the channels which avoids impingement of hot glass against the side walls of the furnace chamber and reduces erosion of these side walls. One or more axially movable electrodes connected to the same terminal project up through the bottom of the furnace between these channels, which electrodes are mounted in special refractory blocks that form platforms above the bottom floor of the furnace and thereby relatively deepen the channels between the electrodes connected to different opposing terminals. These platforms are built up in steps and the edges of their blocks are beveled. Furthermore, the electrodes may be arranged in groups so as to provide one or more separate heating zones connected by these channels. Each electrode is sealed in its refractory block by an inert gas, and it and its block are cooled both by a jacket for coolant liquid around the electrode at least partly recessed in the block, and by a blast of cool air from below and against the jacket, the electrode, and the bottom of the block.

United States Patent 1 Steitz et al.

11 3,757,020 Sept. 4, 1973 ELECTRIC GLASS FURNACE STRUCTURE [75]Inventors: William R. Steitz, Toledo; Robert 0.

Bradley, Ottawa Hills, both of Ohio; Thomas H. Waterworth, Bridgnorth,England [73] Assignees: Toledo Engineering Co., Inc.,

' Toledo, Ohio; Elemelt Limited,

Kingswinford, England [22] Filed: Dec. 23, 1971 [21] Appl. No.: 2ll,l96

Related US. Application Data [63] Continuation-in-part of Ser. No.41,385, May 28,

1970, Pat. No. 3,634,588.

l/l952 Great Britain l3/6 Primary Examiner-Roy N. Envall, Jr.Attorneyl-lugh A. Kirk [5 7] ABSTRACT An electric glass furnace chamberhaving a bottom floor and side walls wherein the floor of the furnace isformed with a cruciform system of channels by means of which moltenglass is withdrawn towards an outlet by opposing flow patterns in thechannels thereby reducing flow patterns in the molten glass above thechannels which avoids impingement of hot glass against the side walls ofthe furnace chamber and reduces erosion of these side walls. One or moreaxially movable electrodes connected to the same terminal project upthrough the bottom of the furnace between these channels, whichelectrodes are mounted in special refractory blocks that form platformsabove the bottom floor of the furnace and thereby relatively deepen thechannels between the electrodes connected to different opposingterminals. These platforms are'built up in steps and the edges of theirblocks are beveled. Furthermore, the electrodes may be arranged ingroups so as to provide one or more separate heating zones connected bythese channels. Each electrode is sealed in its refractory block by aninert gas, and it and its block are cooled both by a jacket for coolantliquid around the electrode at least partly recessed in the block, andby a blast of cool air from below and against the jacket, the electrode,and the bottom of the block.

13 Claims, 4 Drawing Figures ELECTRIC GLASS FURNACE STRUCTURE RELATEDAPPLICATIONS This is a continuation-in-part application of copending[1.8. application Ser. No. 41,385 filed May 28, 1970 by W.R. Steitz etal. now US. Pat. No. 3,634,588.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to electric furnace structures specifically adapted for meltingor treating glass and silica.

2. Description of the Prior Art Electric glass resistance furnaces needto be very carefully made of refractory brick so that once they are putinto operation they will run for several months and preferably severalyears before having to be shut down. Thus it is important that as littlecorrosion and erosion as possible takes place during the life of afurnace.

However, a problem exists in furnaces of this type wherein molten glassis drawn off by way of an outlet channel in the floor of the furnaceextending from a central region of the furnace chamber towards one ofthe side walls and extending generally beneath a heating zone in whichthe glass is traversed by electric currents. The movement of glass in alayer adjacent the floor tends to produce similar movement of a layer ofglass near the surface by an entrainment effect. Whereas the lower layerof molten glass moves outwardly through the outlet of the furnacechamber, the upper stream of molten glass impinges on a side wallportion situated more or less vertically above the outlet and tends toproduce accelerated wear by erosion and like effects locally at thisposition.

Also since the most heat generated in the electrical resistance of themolten glass is along the shortest path between the electrodes, it isdesirable that this shortest path be spaced as far as possible from thebottom surface of the furnace to reduce the erosion on its refractorybricks and blocks.

Also with electrodes spaced apart peripherally around the side walls ofthe furnace and some current flowing between peripherally adjacentelectrodes, it is inevitable that some of the current passes throughlayers of glass contiguous with the side walls and gives rise to heatingand erosion thereof.

An example of an electric glass resistant furnace of the type involvedherein is shown in Cell et al. US. Pat. No. 3,440,321 issued Apr. 22,1969.

To overcome these problems, the bottom wall of the furnace disclosed inthe above mentioned patent to Gell was provided with blocks fonningraised portions through which the electrodes extend, thus raising theshortest distance-between the electrodes in the molten glass above thebottom of the furnace. Withdrawal of glass was effected by way of anoutlet means including an opening of trough-like form in the bottom wallof the furnace leading to an outlet in one of the side walls.

SUMMARY OF THE INVENTION Generally speaking, this invention embodies anovel. electric glass furnace structure which comprises a meltingchamber having side walls and a bottom floor, wherein the floor isformed with a system of crossing or intersecting channels which separatea plurality of electrodes. These electrodes may be separately axiallyand vertically movable and project above the floor through separateplatforms for those of the electrodes connected to different electricalterminals. These platforms may be formed in steps of refractory blockswhich have their exposed edges beveled so as to reduce the amount ofsurface which is in direct contact with the molten glass. The platformsmay define the network of channels distributed over the floor withchannels which feed an outlet means, including a trough, extendingtowards the trough from regions between peripherally adjacentelectrodes, other regions, extending around the electrodes and up toadjacent portions of the side walls, being occupied by the platforms.This network may be so arranged as to include one or more channelstraversing the floor between one pair of opposed side walls, at leastone channel connecting these traversing channels, the troughcommunicating with this connecting channel in aregion centrally thereof.Also a combination of water and air means may be provided for coolingeach electrode and adjacent refractory block assembly.

This network or arrangement of channels which cross beneath each heatingzone formed by four spaced platforms of electrodes, produce at least onepair of opposing flow paths for the molten glass in one channel towardsits intersection with another channel or the trough. This opposing flowtends to produce a stationary pool of molten glass at such intersectionwhich entrains the molten glass above it to continue the stationary poolto the surface of the molten glass, thus reducing erosion on the sidewalls of the furnace due to entrained flow of molten glass in thetrough.

In one form of this invention, the electrodes define separate heatingzones spaced horizontally in the furnace, which zones are connected by achannel in which the molten glass flowing form one zone opposes the flowof the molten glass from the other zone towards a junction from which anoutlet trough may extend.

By the above network or arrangement of channels, molten glass tends tobe withdrawn in a controlled manner from between each set of electrodesbetween which current passes through the glass, and systematic drift orimpingement of upper layers of glass on a side wall of the furnace isminimized. Also the platforms reduce the depth of glass in the regionsbetween the electrodes and the side walls and help to reduce the amountof current flowing in layers of glass adjacent to the side walls. Wherethe depth of glass is greater, namely over the channels, the glass isdrawn away from the side walls by virtue of the glass flow patternpromoted by the channels. Also the current flow through the molten glassis spaced farther from the surface of the floor by the platforms for theelectrodes, so that erosion of the bottom surfaces by an electricallyheated molten glass is reduced.

Directly around each electrode an inert gas seal is provided. Also acooling liquid jacket is provided around each electrode which isinserted into a cavity or recess in the bottom of the refractory blockthrough which the electrode extends. By controlling the flow of theliquid, such as water, through this jacket, one can cause the naturalglass seal, at the end of the inert gas directly around the electrode,to soften so that the electrode may be vertically moved as desired.

In addition to the liquid cooling of the electrodes and the refractoryblocks through which they extend, jets of air are blown against thelower surfaces of the refractory blocks around the electrodes and theircooling jackets to further cool these parts.

OBJECTS AND ADVANTAGES Accordingly it is an object of this invention toincrease the life of an electric furnace by reducing erosion of the sidewalls, caused by flow of molten glass, by controlling such flowincluding the flow for the withdrawal of molten glass from the furnace.

Another object is to increase the distance between the currentconducting heat paths in the molten glass from the surfaces of therefractories in the bottom of the furnace.

A further object is to reduce the thermal shock on the refractoriesaround the electrodes.

BRIEF DESCRIPTION OF THE VIEWS The above mentioned and other features,objects and advantages, and a manner of attaining them are describedmore specifically below by reference to embodiments of thisinventionshown in the accompanying drawings, wherein:

FIG. 1 is a schematic plan view of a resistance electrical glass furnacehaving two spaced heating zones showing a system of channels betweenelectrodes projecting through the bottom thereof, a draw-off channel forthe molten glass in the bottom and part of the riser duct therefrom,together with sawtooth electrical resistance lines between oppositeterminals of the electrodes, with dotted resistance lines for the straycurrents which also occur between the electrodes of other pairs ofterminals;

FIG. 2 is a vertical section taken along jogged line 2 2 of the bottompart of the furnace in FIG. 1 showing the refractory blocks in which theelectrodes are mounted as well as the channels between them and thebottom draw-off trough;

FIG. 3 is a schematic plan view of another embodiment of a resistanceelectrical glass furnace similar to that shown in FIG. 1, but havingonly one heating zone; and

FIG. 4 is a section taken along line 4 4 of FIG. 3 showing an electrodein the riser from the draw-off trough, as well as a schematic means forvertically raising and lowering one of the electrodes in the furnace andthe cooling means therefor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS General Referring to allthe figures in general, and particularly to FIGS. 1 and 3, there areshown the general outlines of two embodiments of electric glass furnacesl and 110. The overall structure of these furnaces and 110 are quitesimilar to each other in many respects and each employ similar elements.Thus these similar elements will be described together and identified bythe same reference characters.

Furnace Tank Construction As shown in FIGS. 1 and 3, the furnaces 10 and110 have rectangular melting chambers or tanks 12 and 1 12 having abottom floor 14 and 114 and side and end walls 16 and 18 for the tank 12(see FIG. 1) and side and end walls 116 and 118 for the tank 112 (seeFIG. 3), respectively, all of which are made of refractory brick.

Floor and Channel Network Each floor 14 and 114 of the melting chambers12 and 112, respectively, is formed with a system of crossing orintersecting channels 20 and 22 for the chamber 12 (see FIG. 1) and 120and 1.22 for the chamber 112 (see FIG. 3). As shown in FIG. 1, thenetwork of channels includes one or more channels 20 traversing thefloor 14 between one pair of opposed side walls 16 and at least onechannel 22 traversing the floor 14 between the end walls 18 andconnecting these traversing channels 20. In the embodiment shown in FIG.3, the channel 120 traverses the floor 114 between the side walls 116and the connecting channel 122 traverses the floor 114 between the endwalls 118.

At the center of each bottom floor or wall 14 and 114 and extending partway across it is a lower outlet or draw off channel or trough 24 whichextends beyond the side wall 16 or 116 through a tunnel 26 into a riser28 and thence into a molten glass distributing chamber 30 (seeparticularly FIG. 4). As shown in FIG. 1 the outlet trough 24 connectswith the channel 22 while in the embodiment shown in FIG. 3 the outlettrough 24 coincides with the traversing channel and intersects with thechannel 122. An electrode 29 may be provided in the riser 28 to keep themolten glass liquid in the tunnel 26 and the distributing chamber 30, ifan when the flow therethrough is reduced.

The Electrodes Referring now to FIGS. 1 and 3, the network ofintersecting channels for each embodiment separates a plurality ofclusters of similar electrodes 32 through 35. These electrodes 32through 35 project above the floors 14 or 114 through platforms 36 intothe molten glass contained in the tank 12 or 1 12, but not above thesurface of the molten glass. These plurality of clusters of electrodes32 through 35 are arranged in groups of four which are relativelyequally spaced with opposite terminals at the ends of the diagonals ofsquares on opposite sides of the intersecting channels 20 and 22 (seeFIG. 1) or 120 and 122 (see FIG. 3). For example, the opposite terminalfor the electrode cluster 32 is in the terminal for the cluster ofelectrodes 35, and in the same square, electrodes 33 are oppositeelectrodes 34. Although three electrodes are shown connected to each ofthe electrical terminals in these embodiments, one or more may beemployed without departing from the general scope of this invention.However, the connection of more than one electrode to each terminalinsures continuous operation in the event one or two of the electrodesat that terminal fails during the several months or years operation ofthe furnace. There is also shown schematically full sawtooth resistancelines diagonally across each square from the central electrode of eachgroup to show in what direction the most heating electrical currentnormally flows through the molten glass in the tank when it is inoperation. Nevertheless there is also some heating current flow betweenthe electrodes 32 and 33, 32 and 34, 33 and 35, and 34 and 35. Thus heatis induced into the molten glass between all of the different electrodeterminals or groups of electrodes 32 through 35 in each heating zone.

The Platforms Referring back to FIGS. 1, 2 and 3, each of the electrodes32 through 35 is individually mounted in separate special refractoryblocks 38 or 40, which blocks in turn seat in additional specialrefractory blocks 42, the upper faces of which blocks 38, 40 and 42 arestepped above the floor or surface of the floor 14 or 114 in the tank 12or 112, respectively, so as to help define the channels or troughs 20and 22 pr 12 and 122 which cross each other at the center of the groupsor squares of the electrodes in their respective tanks 12 or 112. Thestepped upper edges of the blocks 38, 40, and 42 may be beveled at theirexposed comer edges to reduce the amount of the surface that is actuallyin contact with the molten glass in the tank adjacent their respectiveelectrodes. Thus, the electrodes at each terminal are raised onplatforms above the bottom surface of the tank so that electricalresistance between the electrodes connected to different terminals isshorter directly through the liquid than along the bottom surface of thetank. This reduces the amount of heat which is created on the skin layerof the molten glass against the refractories forming the bottom surfaceof the tank and upper surfaces of the blocks 38, 40 and 42. Accordingly,most of the heat from the electrical current goes directly into themolten glass, increasing the efficiency of the operation of the furnace,as well as increasing the life of the refractories making up its bottom,and specifically those blocks 38 and 40 directly supporting theelectrodes. The platforms reduce the depth of glass between theelectrode clusters and the side walls. At these localities thecross-sectional area of glass presented to current flow in layersadjacent to an extending along the side walls tends to be reduced. Wherethe depth has full value as over the channels 20, 22, 120, 122, theheated glass is drawn away from the side walls and erosion is reduced.

The Heating Zones In the embodiment shown in FIG. 1, a group ofelectrodes 32 through 35 is provided in each end region of the generallyrectangular furnace chamber 12, each of which groups defines a heatingzone traversed by current represented by the full and dotted sawtoothresistance lines already mentioned. Between these two zones there is anintervening zone which is not traversed by main heating currents. Somecurrent will flow in this region, e.g. sufficient to provide heating tocompensate at least partly for heat losses. The cruciform shaped channelsystem previously described in each heating zone includes the channels20 and 22 which extend from positions adjacent the side walls 16 and endwalls 18 and act as collector channels withdrawing molten glass from theperiphery of each zone. The flow in these channels 20 and 22 thuspromotes down flow of cool glass over the interior surfaces of the sidewalls bounding each heating zone.

Withdrawal of molten glass from each heating zone takes place along thechannel 22 of the system towards its mid region between the two heatingzones. Thus the flow along this channel 22 takes place in oppositedirections from each heating zone, so that there is a tendency to form astationary pool of glass at its mid region or intervening zone.

From this stationary pool the outlet or draw-off channel 24 extends tothe tunnel 26. If, therefore, there is any entrainment of surface glassin a direction towards the side wall 16 of the furnace chamber 12 abovethe channel 24, the portion of the side wall against which the glassimpinges will be relatively cool since it is situated remotely from bothof the heating zones.

Furthermore, any heated glass which migrates in the surface layer fromeach heating zone towards the mid region of the intervening zone byvirtue of entrainment with glass withdrawn along the feeder channels 22towards outlet channels 24, produces an accumulation or pool at thesurface of the intervening zone in the central region thereof. Surplusglass thus tends to flow outwardly in a more or less uniform manner andmigrate back to the heating zones without giving rise to any severelocal impingement on the side walls 16 above the outlet channel 24.

Similarly, in the embodiment shown in FIG. 3, the flow of molten glassin channel 122 is from the side walls 118 towards the center of theheating zone to form a relatively stationary pool in the center of thisheating zone. Furthermore, the outlet channel 24 from this pool does notmaterially increase the flow of molten glass against the side 116 aboveit by entrainment.

Electrode Mounting and Cooling Referring now to FIG. 4, there isschematically shown one of the electrodes 32 projecting below the bottomwall of the tank 112 and resting in a socket 44 at the upper end of ascrew 46 which may be raised and lowered via a drive gear and motormechanism 48. Each one of the separate electrodes 32 through 35 are soconnected to these devices 44, 46 and 48 for their vertical movement.Above each socket 44 there is shown a clamp means 50 by which anelectrical connection is made to each electrode.

Also schematically shown is a duct 54 which passes a liquid coolant,such as water, through a jacket 55 partly inserted in the block 38 andsurrounding the electrode 34 for regulating the temperature of theelectrode to cause the molten glass to seal its upper end in the block38. Also this serves to keep the electrode and its surroundingrefractory block 38 cool.

Also in FIG. 4 there is schematically shown a duct 52 which directs aninert gas under pressure into the space in the block 38 whichaccommodates the jacket. This is to prevent air or oxidizing gasespermeating the block and reaching the hot part of the electrode.

In addition to this liquid coolant 54, there is also provided a blast ofcooling air via a duct 56, which is directed up into the bottom of theblocks 38 and 40 and around the outside of the jacket 55 and electrode32 to cool further not only the electrode 32 but also the outer andlower ends of the refractory blocks 38 and 40'further reducing thechances of thermal shock to these parts. For example, in oneinstallation, as much as 500 cubic feet of air per minute is blown oneach group of electrodes.

The cooling of the blocks 38 and 40 enables the vertical heat gradientthrough these blocks to be maintained at a value which conforms at leastapproximately to that of the associated electrode 32 and thereby avoidsor minimizes risk of cracking or disrupting the means sealing theelectrodes with respect to the blocks.

Although the different features of this invention are related, they maybe used separately or in different combinations if desired, withoutdeparting from the scope of this invention.

While there is described above the principles of this invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of this invention.

We claim:

1. An electric glass furnace having a bottom and side walls, electrodesprojecting up through said bottom, and a withdrawal trough in saidbottom having an outlet in one of said side walls, the improvementcomprising: channels in the bottom of said furnace leading from thewalls through regions between the electrodes connected to differentterminals to said trough which is connected to and between the ends ofone of said channels whereby opposing molten glass flow occurs in saidchannel towards this connection to produce a stationary pool of moltenglass thereabove reducing erosion of said side walls due to entrainmentflow above said trough, the entire floor surface in regions around saidelectrodes and between said electrodes and adjacent portions of the sidewalls being higher than the bottoms of said channels.

2. A furnace according to claim 1 wherein said channels and troughintersect at right angles to each other to form a cruciform pattern inthe bottom of said furnace.

3. A furnace according to claim 1 including platforms at the corners ofsaid intersecting channels and trough for mounting said electrodes abovethe bottom floor of said furnace. Y

4. A furnace according to claim 1 including means for cooling saidelectrodes and the refractory blocks surrounding them, and wherein saidmeans for cooling comprises both liquid and air.

5. A furnace according to claim 1 wherein said withdrawal trough extendsbeyond said one side wall of said furnace into a riser duct, and whereinsaid riser duct includes an electrode extending through the bottom ofthe trough under said riser duct.

6. An electric glass furnace comprising:

A. a melting chamber with side walls and a floor,

B. a plurality of electrodes separately axially and vertically movableprojecting above said floor,

C. separate platforms for those of the electrodes which are connected todifferent electrical tenninals, from which platforms said electrodesproject vertically, said platforms being each formed of a plurality ofrefractory blocks forming steps to the top of said platforms from thebottom of a network of channels defined by said platforms anddistributed over said floor, said channels extending between saidelectrodes connected to said different terminals, and said networkincluding a plurality of channels traversing the floor between one pairof opposed side walls and at least one channel connccting said pluralityof channels,

D. outlet means communicating with said network in a region centrallythereof, and

E. means for cooling each electrode and refractory block assembly.

7. A furnace according to claim 6 wherein said blocks have beveled edgestoward the bottoms of said 6 B. a plurality of electrodes separatelyaxially and vertically movable projecting above said floor,

C. separate platforms for the electrodes connected to differentelectrical terminals, each said platform being formed of refractoryblocks comprising:

1. a central block portion projecting above said floor and having avertical aperture for each said electrode, and

2. a seating block portion around and for said central block portion andprojecting above said floor, said seating block portion substantiallybridging the vertical distance between said floor and the top surface ofsaid central block portion,

D. means for sealing said electrodes in said central block portions, and

E. means for cooling both said electrodes and block portions in thelatter case below said floors.

9. An electric glass furnace according to claim 8 wherein said means forcooling said electrode comprises a water jacket around the lower end ofsaid electrode, and said means for cooling said block portions comprisesmeans for blowing air thereon.

10. An electric glass furnace according to claim 8 wherein said meansare provided for supplying an inert gas around said electrode at theunderside of said central block portion to provide a sealing againstperme' ation by an oxidizing gas.

11. In an electric glass heating furnace comprising a chamber forcontaining a body of molten glass having a floor and upstanding sidewalls and an outlet positioned for withdrawing glass from the bottom ofsaid chamber, and electrode means, the improvement comprising:

A. said electrode means defining separate respective heating zonessituated in horizontally spaced regions of the chamber,

B. said chamber having open channel means in said floor defining awithdrawal flow path for the glass including feeder branches extendinggenerally horizontally from the walls of respective ones of said zonesadjacent to the floor of the chamber along mutually opposing directionstowards a junction, and including an outlet branch extending from saidjunction to said outlet.

12. An electric glass furnace according to claim 11 wherein:

A. said electrode means are so positioned as to to define an interveningzone between said heating zones and bounded partly by the latter andpartly by at least one side wall portion of the chamber,

B. said channel means defining said withdrawal flow path including:

a. for each of said heating zones collector branches extending frompositions adjacent to the side walls of the chamber bounding saidheating zone towards a central region of said heating zone, and furtherincluding a feeder branch extending towards and opposing thecorresponding feede branch leading to said junction,

b. an outlet trough extending from said junction in a directiontransverse to the approach directions of said feeder channels towardssaid one side wall portion as viewed in plan.

13. An electric furnace according to wherein: j

A. the chamber is of generally rectangular form in plan,

claim 12 9 B. the electrode means are positioned to define re- D. saidfeeder channels extend generally parallel to spective ones P saidheating zqnes l Plthe larger plan dimension of the channel and lieportions of said chamber leaving said intervening media"), of thesmaller plan-dimension thereof,

9 in between said heating zones in a central B. said outlet troughextends from said junction in a gion of the length of the chamber,

C. said collector channels extend in each of said heatgenerally parallelto the smalier d1- ing zones from positions adjacent to the midremenslon of the chamber towards the region of gions of said wallportions of th h b b d a side wall portion bounding the interveningzone. ing said zone towards the central region thereof,

1. An electric glass furnace having a bottom and side walls, electrodesprojecting up through said bottom, and a withdrawal trough in saidbottom having an outlet in one of said side walls, the improvementcomprising: channels in the bottom of said furnace leading from thewalls through regions between the electrodes connected to differentterminals to said trough which is connected to and between the ends ofone of said channels whereby opposing molten glass flow occurs in saidchannel towards this connection to produce a stationary pool of moltenglass thereabove reducing erosion of said side walls due to entrainmentflow above said trough, the entire floor surface in regions around saidelectrodes and between said electrodes and adjacent portions of the sidewalls being higher than the bottoms of said channels.
 2. A furnaceaccording to claim 1 wherein said channels and trough intersect at rightangles to each other to form a cruciform pattern in the bottom of saidfurnace.
 2. a seating block portion around and for said central blockportion and projecting above said floor, said seating block portionsubstantially bridging the vertical distance between said floor and thetop surface of said central block portion, D. means for sealing saidelectrodes in said central block portions, and E. means for cooling bothsaid electrodes and block portions in the latter case below said floors.3. A furnace according to claim 1 including platforms at the corners ofsaid intersecting channels and trough for mounting said electrodes abovethe bottom floor of said furnace.
 4. A furnace according to claim 1including means for cooling said electrodes and the refractory blockssurrounding them, and wherein said means for cooling comprises bothliquid and air.
 5. A furnace according to claim 1 wherein saidwithdrawal trough extends beyond said one side wall of said furnace intoa riser duct, and wherein said riser duct includes an electrodeextending through the bottom of the trough under said riser duct.
 6. Anelectric glass furnace comprising: A. a melting chamber with side wallsand a floor, B. a plurality of electrodes separately axially andvertically movable projecting above said floor, C. separate platformsfor those of the electrodes which are connected to diffErent electricalterminals, from which platforms said electrodes project vertically, saidplatforms being each formed of a plurality of refractory blocks formingsteps to the top of said platforms from the bottom of a network ofchannels defined by said platforms and distributed over said floor, saidchannels extending between said electrodes connected to said differentterminals, and said network including a plurality of channels traversingthe floor between one pair of opposed side walls and at least onechannel connecting said plurality of channels, D. outlet meanscommunicating with said network in a region centrally thereof, and E.means for cooling each electrode and refractory block assembly.
 7. Afurnace according to claim 6 wherein said blocks have beveled edgestoward the bottoms of said channels.
 8. An electric glass furnacecomprising: A. a melting chamber with side walls and a floor, B. aplurality of electrodes separately axially and vertically movableprojecting above said floor, C. separate platforms for the electrodesconnected to different electrical terminals, each said platform beingformed of refractory blocks comprising:
 9. An electric glass furnaceaccording to claim 8 wherein said means for cooling said electrodecomprises a water jacket around the lower end of said electrode, andsaid means for cooling said block portions comprises means for blowingair thereon.
 10. An electric glass furnace according to claim 8 whereinsaid means are provided for supplying an inert gas around said electrodeat the underside of said central block portion to provide a sealingagainst permeation by an oxidizing gas.
 11. In an electric glass heatingfurnace comprising a chamber for containing a body of molten glasshaving a floor and upstanding side walls and an outlet positioned forwithdrawing glass from the bottom of said chamber, and electrode means,the improvement comprising: A. said electrode means defining separaterespective heating zones situated in horizontally spaced regions of thechamber, B. said chamber having open channel means in said floordefining a withdrawal flow path for the glass including feeder branchesextending generally horizontally from the walls of respective ones ofsaid zones adjacent to the floor of the chamber along mutually opposingdirections towards a junction, and including an outlet branch extendingfrom said junction to said outlet.
 12. An electric glass furnaceaccording to claim 11 wherein: A. said electrode means are so positionedas to to define an intervening zone between said heating zones andbounded partly by the latter and partly by at least one side wallportion of the chamber, B. said channel means defining said withdrawalflow path including: a. for each of said heating zones collectorbranches extending from positions adjacent to the side walls of thechamber bounding said heating zone towards a central region of saidheating zone, and further including a feeder branch extending towardsand opposing the corresponding feeder branch leading to said junction,b. an outlet trough extending from said junction in a directiontransverse to the approach directions of said feeder channels towardssaid one side wall portion as viewed in plan.
 13. An electric furnaceaccording to claim 12 wherein: A. the chamber is of generallyrectangular form in plan, B. the electrode means are positioned todefine respective ones of said heating zones in opposite end portions ofsaid chamber leaving said intervening zone in between said heating zonesin a central region of the length of the chamber, C. said collectorchannels extend in each of said heating zones from positions adjacent tothe mid regions of said wall portions of the chamber bounding said zonetowards the central region thereof, D. said feeder channels extendgenerally parallel to the larger plan dimension of the channel and liemedially of the smaller plan dimension thereof, E. said outlet troughextends from said junction in a direction generally parallel to thesmaller plan dimension of the chamber towards the mid region of a sidewall portion bounding the intervening zone.